Fabrication method of semiconductor integrated circuit device

ABSTRACT

A method of fabrication of a semiconductor integrated circuit device, calls for disposing, in an ultrapure water preparing system, UF equipment having therein a UF module which has been manufactured by disposing, in a body thereof, a plurality of capillary hollow fiber membranes composed of a polysulfone membrane or polyimide membrane, bonding the plurality of hollow fiber membranes at end portions thereof by hot welding, and by this hot welding, simultaneously adhering the hollow fiber membranes to the body. Upon preparation of ultrapure water to be used for the fabrication of the semiconductor integrated circuit device, it is possible to prevent run-off of ionized amine into the ultrapure water.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a method of fabrication of asemiconductor integrated circuit device; and, more particularly, theinvention relates to a technique for improving the quality of pure waterto be used for the fabrication of a semiconductor integrated circuitdevice.

[0002] Upon fabrication of a semiconductor device, includingmicrofabrication of an integrated circuit, it is required to removeimpurities from the surface or interface of a semiconductor wafer (whichwill hereinafter simply be called a “wafer”) by cleaning, therebymaintaining the cleanness of the wafer. Foreign matter on a wafer maycause disconnection or short-circuit of wiring. In particular, heavymetal components must be removed completely, because they have a seriousinfluence on the electrical properties of the device.

[0003] Pure water is used for washing a wafer surface to remove achemical solution after the wafer has been cleaned therewith or wetetched therewith, thereby making the wafer clean; or pure water is usedfor preparing a chemical solution used in a cleaning or wet etchingstep. Pure water used in such a step is prepared by removing, from rawwater, fine particles, organic matter and high molecular ions by use ofan RO (reverse osmosis) unit equipped with an RO (Reverse Osmosis)membrane, removing the other ions by using an ion exchange resin, andthen removing fine particles and living bacteria, which are still in theraw water after the action of the RO unit and ion exchange resin, usingUF equipment (ultrafiltration equipment). A process for preparation ofsuch pure water is disclosed, for example, in Japanese Unexamined PatentApplication No. Hei 4(1992)-78483. Also, Japanese Unexamined PatentApplication No. Hei 10(1998)-216721 discloses a technique for removinganions, which are too small to pass through UF equipment, using an anionadsorption membrane apparatus disposed downstream of the UF equipment.

SUMMARY OF THE INVENTION

[0004] The present inventors have investigated the possibility toconstruct a system for obtaining pure water having high purity (whichwill hereinafter be called “ultrapure water”) to be used for thefabrication of a semiconductor integrated circuit device. During theinvestigation, they found that the problems as described below occur.

[0005] UF equipment is used in the final step of the preparation ofultrapure water. The UF equipment has a moduled filter obtained bybundling a plurality of capillary hollow fiber membranes using anadhesive which contains an epoxy resin as a raw material. This filterneeds periodic replacement with a new one owing to the life of itsmaterial. The adhesive used for bundling the hollow fiber membranescontains an amine, and a portion of this amine has been ionized. Whenwater is caused to pass through this UF equipment, after replacement ofthe filter, this ionized amine is hydrolyzed and is transferred into theultrapure water. If ultrapure water containing this ionized amine isused, for example, for cleaning a wafer just before the formation of agate oxide film of a MISFET (Metal Insulator Semiconductor Field EffectTransistor), the Si (silicon) which constitutes the wafer is inevitablyetched by this ionized amine, resulting in the formation of anunevenness on the interface between the gate insulating film and thewafer after formation of the gate insulating film. When the MISFETformed under such a state constitutes a memory cell of an electricallyerasable programmable read only memory (EEPROM; which will hereinafterbe called “flash memory”), the breakdown voltage of the gate insulatingfilm is lowered, leading to the problem of a deterioration in the writecharacteristics to the memory cell, as well as the erase characteristicsthereof. Even if the above-described MISFET is used for semiconductordevices other than the memory cell of a flash memory, an electriccurrent between the source and the drain is disturbed, causing a failurein the characteristics.

[0006] A test made by the present inventors has revealed that theionized amine comes also from the RO unit and ion exchange resin. Thereis a possibility that such an ionized amine coming from a place otherthan the UF equipment flows into the ultrapure water.

[0007] An object of the present invention is to prevent run-off of anionized amine into ultrapure water upon preparation of the ultrapurewater to be used for the fabrication of a semiconductor integratedcircuit device.

[0008] The above-described and the other objects and novel features ofthe present invention will be apparent from the following descriptionherein and the accompanying drawings.

[0009] Typical aspects of the invention, among those disclosed in thepresent application, will be summarized briefly below.

[0010] In one aspect of the present invention, there is provided amethod of fabrication of a semiconductor integrated circuit device,which comprises introducing indifferent water, as first raw materialwater, into a primary pure water system having a primary purifyingsystem; introducing, as second raw material water, the primary purewater, which has been obtained by purification through the primarypurifying system, into a secondary pure water circulating system havinga secondary purifying system; and feeding a first wet treatmentapparatus with the secondary pure water which has been obtained bypurification through the secondary purifying system, thereby subjectinga semiconductor integrated circuit wafer to first wetting treatment,wherein, in the secondary purifying system, there are an ion removingstep through use of an ion removing filter, a foreign particle removingstep through use of an ultrafiltration filter, and a step of feeding thefirst wetting treatment apparatus with pure water which has passedthrough the ion removing filter and the ultrafiltration filter, and bythe time when the pure water is fed to the first wetting treatmentapparatus, ionized amines or ionized amine substances have been removedfrom the secondary pure water to such an extent as not to affect thecharacteristics of the semiconductor integrated circuit device.

[0011] In another aspect of the present invention, there is alsoprovided a method of fabrication of a semiconductor integrated circuitdevice, which comprises introducing, as first raw material water,indifferent water into a primary pure water system having a primarypurifying system; introducing, as second raw material water, the primarywater, which has been obtained through the primary purifying system,into a secondary pure water circulating system having a secondarypurifying system; and feeding a first wetting treatment apparatus withthe secondary pure water which has been obtained by purification of thesecond raw material water through the secondary purifying system,thereby subjecting a semiconductor integrated circuit wafer to firstwetting treatment; wherein, in the secondary purifying system, there area step of removing foreign particles from pure water through use of anultrafiltration filter; a step of removing ions from the pure water,which has passed through the ultrafiltration filter, by use of amembrane type ion removing filter; and a step of feeding the firstwetting treatment apparatus with the pure water which has passed throughthe ion removing filter.

[0012] In a further aspect of the present invention, there is alsoprovided a method of fabrication of a semiconductor integrated circuitdevice, which comprises introducing, as first raw material water,indifferent water into a primary pure water system having a primarypurifying system; introducing, as second raw material water, the primarywater, which has been obtained through the primary purifying system,into a secondary pure water circulating system having a secondarypurifying system; and feeding a first wetting treatment apparatus withsecondary pure water which has been obtained by purification through thesecondary purifying system, thereby subjecting a semiconductorintegrated circuit wafer to first wetting treatment; wherein, in thesecondary purifying system, there are a step of removing foreignparticles from pure water through use of an ultrafiltration filterdisposed in the secondary purifying system; a step of removing ions fromthe pure water, which has passed through the ultrafiltration filter, byuse of a membrane type ion removing filter that is disposed outside ofthe secondary pure water circulating system; and a step of feeding thefirst wetting treatment apparatus with the pure water which has passedthrough the ion removing filter.

[0013] In a still further aspect of the present invention, there is alsoprovided a method of fabrication of a semiconductor integrated circuitdevice, which comprises introducing, as first raw material water,indifferent water into a primary pure water system having a primarypurifying system; introducing, as second raw material water, the primarywater, which has been obtained through the primary purifying system,into a secondary pure water circulating system having a secondarypurifying system; and feeding a first wetting treatment apparatus withthe secondary pure water which has been obtained by purification throughthe secondary purifying system, thereby subjecting a semiconductorintegrated circuit wafer to first wetting treatment, wherein: in thesecondary purifying system, there are a step of removing ions from purewater through use of an ion removing filter that is disposed inside ofthe secondary purifying system; a step of causing the pure water, whichhas passed through the ion removing filter, to pass through a heatwelding type ultrafiltration filter that is disposed inside of thesecondary purifying system, thereby removing foreign particles from thepure water; and a step of feeding the first wetting treatment apparatuswith the pure water which has passed through the ultrafiltration filter.

[0014] In a still further aspect of the present invention, there is alsoprovided a method of fabrication of a semiconductor integrated circuitdevice, which comprises introducing, as first raw material water,indifferent water into a primary pure water system having a primarypurifying system; introducing, as second raw material water, the primarywater, which has been obtained through the primary purifying system,into a secondary pure water circulating system having a secondarypurifying system; and feeding a first wetting treatment apparatus withthe secondary pure water which has been obtained by purification throughthe secondary purifying system, thereby subjecting a semiconductorintegrated circuit wafer to first wetting treatment; wherein, in thesecondary purifying system, there are a step of removing ions by use ofan ion removing filter, a step of removing foreign particles through aultrafiltration filter, and a step of feeding the first wettingtreatment apparatus with the pure water which has passed through the ionremoving filter and the ultrafiltration filter, and wherein theultrafiltration filter is disposed at a position permitting selfcleaning.

[0015] The outline of other examples of the invention described in thepresent application will be described below:

[0016] Item 1: A method of fabrication of a semiconductor integratedcircuit device, which comprises cleaning a semiconductor substrate orpreparing a chemical solution with pure water prepared by a pure waterpreparation step having the sub-steps of:

[0017] (a) removing first foreign matter from raw water containingforeign matter, and

[0018] (b) removing, after the sub-step (a), foreign matter other thanthe first foreign matter from the raw water by using a first apparatusequipped with a filter formed by bonding a plurality of hollow fibermembranes at the end portions thereof, wherein the hollow fibermembranes permit passage of only substances having a molecular weightnot greater than a predetermined value, the plurality of hollow fibermembranes are heat welded or bonded with an amine-free material, and thefirst apparatus removes the foreign matter other than the first foreignmatter from the raw water by causing the raw water to pass through thefilter.

[0019] Item 2: The method of fabrication of a semiconductor integratedcircuit device according to Item 1, wherein the hollow fiber statemembranes are each composed mainly of polysulfone or polyimide.

[0020] Item 3: The method of fabrication of a semiconductor integratedcircuit device according to Item 1, further comprising heat treating thesemiconductor substrate after the cleaning step, thereby forming a gateinsulating film.

[0021] Item 4: The method of fabrication of a semiconductor integratedcircuit device according to Item 3, wherein the gate insulating film isformed to have a film thickness of 20 nm or less.

[0022] Item 5: The method of fabrication of a semiconductor integratedcircuit device according to Item 1, further comprising, after thecleaning step, forming a nonvolatile memory cell, the nonvolatile memorycell forming step having the following sub-steps:

[0023] (c) heat treating the semiconductor substrate, thereby forming agate insulating film,

[0024] (d) forming thereover a first conductive film,

[0025] (e) forming thereover a first insulating film,

[0026] (f) forming thereover a second conductive film,

[0027] (g) patterning the second conductive film, thereby forming acontrol gate electrode made thereof, and

[0028] (h) patterning the first insulating film and the first conductivefilm, thereby forming a floating gate electrode made of the firstconductive film.

[0029] Item 6: The method of fabrication of a semiconductor integratedcircuit device according to Item 5, wherein the gate insulating film isformed to have a thickness of 10 nm or less.

[0030] Item 7: The method of fabrication of a semiconductor integratedcircuit device, which comprises:

[0031] (a) removing first foreign matter from raw water containingforeign matter,

[0032] (b) after the step (a), removing foreign matter other than thefirst foreign matter from the raw water by using a first apparatusequipped with a filter formed by bonding a plurality of hollow fibermembranes at end portions thereof, and

[0033] (c) after the step (b), cleaning a semiconductor substrate orpreparing a chemical solution with pure water prepared by causing theraw water to pass through a first filter made of a hollow-fiber-typefilter membrane having an ion exchange radical, thereby removing ionizedamines from the raw water, wherein, the first apparatus is capable ofremoving foreign matter other than the first foreign matter from the rawwater by causing the raw water to pass through the filter.

[0034] Item 8: The method of fabrication of a semiconductor integratedcircuit device according to Item 7, wherein the step (a) includes asub-step of removing ions from the raw water through a second filtermade of an ion exchange resin having an ion exchange radical or ahollow-fiber-type filter membrane having an ion exchange radical.

[0035] Item 9: The method of fabrication of a semiconductor integratedcircuit device according to Item 7, which further comprises forming agate insulating film by heat treating the semiconductor substrate aftercleaning.

[0036] Item 10: The method of fabrication of a semiconductor integratedcircuit device according to Item 9, wherein the gate insulating film isformed to have a film thickness of 20 nm or less.

[0037] Item 11: The method of fabrication of a semiconductor integratedcircuit device according to Item 7, which further comprises forming anonvolatile memory cell after the cleaning step, the nonvolatile memorycell forming step having the following sub-steps:

[0038] (c) heat treating the semiconductor substrate, thereby forming agate insulating film,

[0039] (d) forming thereover a first conductive film,

[0040] (e) forming thereover a first insulating film,

[0041] (f) forming thereover a second conductive film,

[0042] (g) patterning the second conductive film to form a control gateelectrode made of the second conductive film, and

[0043] (h) patterning the first insulating film and first conductivefilm to form a floating gate electrode made of the first conductivefilm.

[0044] Item 12: The method of fabrication of a semiconductor integratedcircuit device according to Item 11, wherein the gate insulating film isformed to have a thickness of 10 nm or less.

[0045] Item 13: A method of fabrication of a semiconductor integratedcircuit device, which comprises cleaning a semiconductor substrate orpreparing a chemical solution with pure water prepared through a purewater preparing step, comprising the sub-steps of:

[0046] (a) removing first foreign matter from raw water containingforeign matter, and

[0047] (b) after the step (a), removing foreign matter other than thefirst foreign matter by use of a first apparatus equipped with a filterformed by bonding a plurality of hollow fiber membranes at end portionsthereof, wherein the sub-step (a) further comprises removing ions fromthe raw water through use of a second filter made of a hollow-fiber-typefilter membrane having an ion exchange radical.

[0048] Item 14: The method of fabrication of a semiconductor integratedcircuit device according to Item 13, wherein the semiconductor substrateis heat treated after the cleaning step, thereby forming a gateinsulating film.

[0049] Item 15: The method of fabrication of a semiconductor integratedcircuit device according to Item 14, wherein the gate insulating film isformed to have a thickness of 20 nm or less.

[0050] Item 16: The method of fabrication of a semiconductor integratedcircuit device according to Item 13, which further comprises forming anonvolatile memory cell after the cleaning step, thenon-volatile-memory-cell forming step including the following sub-steps:

[0051] (c) heat treating the semiconductor substrate, thereby forming agate insulating film,

[0052] (d) forming thereover a first conductive film,

[0053] (e) forming thereover a first insulating film,

[0054] (f) forming thereover a second conductive film,

[0055] (g) patterning the second conductive film to form a control gateelectrode made of the second conductive film, and

[0056] (h) patterning the first insulating film and first conductivefilm to form a floating gate electrode made of the first conductivefilm.

[0057] Item 17: The method of fabrication of a semiconductor integratedcircuit device according to Item 16, wherein the gate insulating film isformed to have a film thickness of 10 nm or less.

[0058] Item 18: A method of fabrication of a semiconductor integratedcircuit device, which comprises cleaning a semiconductor substrate orpreparing a chemical solution with pure water prepared through a purewater preparing step comprising the sub-steps of:

[0059] (a) removing first foreign matter from raw water containingforeign matter, and

[0060] (b) after the step (a), removing foreign matter other than thefirst foreign matter by use of a first apparatus equipped with a filterformed by bonding a plurality of hollow fiber membranes at end portionsthereof; wherein, in a pathway for sending the pure water from the firstapparatus to an apparatus in which the cleaning step or chemicalsolution preparing step is conducted, a first filter made of ahollow-yarn type filter membrane having an ion exchange radical or anion exchange resin having an ion exchange radical is disposed; and

[0061] wherein ionized amines are removed from the pure water throughuse of the first filter.

[0062] Item 19: The method of fabrication of a semiconductor integratedcircuit device according to Item 18, further comprising heat treatingthe semiconductor substrate after the cleaning step, thereby forming agate insulating film.

[0063] Item 20: The method of fabrication of a semiconductor integratedcircuit device according to Item 19, wherein the gate insulating film isformed to have a film thickness of 20 nm or less.

[0064] Item 21: The method of fabrication of a semiconductor integratedcircuit device according to Item 18, which further comprises forming anonvolatile memory cell after the cleaning step, thenon-volatile-memory-cell forming step including:

[0065] (c) heat treating the semiconductor substrate, thereby forming agate insulating film,

[0066] (d) forming thereover a first conductive film,

[0067] (e) forming thereover a first insulating film,

[0068] (f) forming thereover a second conductive film,

[0069] (g) patterning the second conductive film to form a control gateelectrode made of the second conductive film, and

[0070] (h) patterning the first insulating film and first conductivefilm to form a floating gate electrode made of the first conductivefilm.

[0071] Item 22: The method of fabrication of a semiconductor integratedcircuit device according to Item 21, wherein the gate insulating film isformed to have a film thickness of 10 nm or less.

[0072] Item 23: A method of fabrication of a semiconductor integratedcircuit device, which comprises cleaning a semiconductor substrate orpreparing a chemical solution with pure water prepared through use of apure water preparing step, comprising sub-steps of:

[0073] (a) removing first foreign matter from raw water containingforeign matter, and

[0074] (b) after the step (a), removing foreign matter other than thefirst foreign matter by use of a plurality of first apparatuses eachequipped with a filter formed by bonding a plurality of hollow fibermembranes at end portions thereof, wherein:

[0075] the step (a) further comprises:

[0076] (a1) removing ions from the raw water by use of a second filtermade of an ion exchange resin having an ion exchange radical or ahollow-fiber-type filtration membrane having an ion exchange radical;

[0077] the step (a) is followed by at least one of the sub-steps of:

[0078] (c) causing a portion of the raw water, which has passed throughthe second filter, to pass through a new one of the first apparatus or anew one of the second filter and then feeding the resulting purifiedwater to the second filter, and

[0079] (d) causing the residue of the pure water, after the cleaningstep or chemical-solution-preparing step, to pass through at least oneof a new one of the first apparatus or a new one of the second filter,and then feeding to the second filter; and

[0080] the steps (c) and/or (d) are carried out for a predeterminedterm.

[0081] Item 24. The method of fabrication of a semiconductor integratedcircuit device according to Item 23, further comprising forming a gateinsulating film by heat treating the semiconductor substrate after thecleaning step.

[0082] Item 25. The method of fabrication of a semiconductor integratedcircuit device according to Item 24, wherein the gate insulating film isformed to have a film thickness of 20 nm or less.

[0083] Item 26. The method of fabrication of a semiconductor integratedcircuit device according to Item 23, which further comprises forming anonvolatile memory cell after the cleaning step, thenon-volatile-memory-cell forming step including:

[0084] (c) heat treating the semiconductor substrate, thereby forming agate insulating film,

[0085] (d) forming thereover a first conductive film,

[0086] (e) forming thereover a first insulating film,

[0087] (f) forming thereover a second conductive film,

[0088] (g) patterning the second conductive film to form a control gateelectrode made of the second conductive film, and

[0089] (h) patterning the first insulating film and the first conductivefilm to form a floating gate electrode made of the first conductivefilm.

[0090] Item 27: The method of fabrication of a semiconductor integratedcircuit device according to Item 26, wherein the gate insulating film isformed to have a film thickness of 10 nm or less.

BRIEF DESCRIPTION OF THE DRAWINGS

[0091]FIG. 1 is a fragmentary cross-sectional view illustrating a stepin the fabrication of a semiconductor integrated circuit deviceaccording to one embodiment of the present invention;

[0092]FIG. 2 is a fragmentary cross-sectional view of the semiconductorintegrated circuit device during the fabrication step following the stepof FIG. 1;

[0093]FIG. 3 is a fragmentary cross-sectional view of the semiconductorintegrated circuit device during the fabrication step following the stepof FIG. 2;

[0094]FIG. 4 is a schematic diagram illustrating the system used inpreparing ultrapure water to be used for the fabrication of thesemiconductor integrated circuit device according to the one embodimentof the present invention;

[0095]FIG. 5 is a schematic diagram illustrating details of theultrapure water preparing system illustrated in FIG. 4;

[0096]FIG. 6 is a schematic cross-sectional view of a UF module of UFequipment included in the system used on the preparation of ultrapurewater to be used for the fabrication of the semiconductor integratedcircuit device according to the one embodiment of the present invention;

[0097]FIG. 7 is a fragmentary cross-sectional view of the UF module,taken along line A-A in FIG. 6;

[0098]FIG. 8 is a schematic diagram of a hollow fiber membraneconstituting the UF module illustrated in FIG. 6;

[0099]FIG. 9 is a schematic diagram of an ion filter to be disposeddownstream of the UF equipment included in the system for preparingultrapure water to be used for the fabrication of the semiconductorintegrated circuit device according to the one embodiment of the presentinvention;

[0100]FIG. 10 is a fragmentary cross-sectional view illustrating howions are trapped by the ion filter illustrated in FIG. 9;

[0101]FIG. 11 is a diagram which illustrates one example of the ionfilter illustrated in FIG. 9;

[0102]FIG. 12 is a diagram which illustrates one example of the ionfilter illustrated in FIG. 9;

[0103]FIG. 13 is a diagram which illustrates another example of the ionfilter illustrated in FIG. 9;

[0104]FIG. 14 is a diagram which illustrates a further example of theion filter illustrated in FIG. 9;

[0105]FIG. 15 is a schematic diagram illustrating the constitution ofthe UF equipment included in the system for preparing ultrapure water tobe used for the fabrication of the semiconductor integrated circuitdevice according to the one embodiment of the present invention;

[0106]FIG. 16 is a schematic diagram for illustrating an anion deminerand a cation deminer included in the system for preparing ultrapurewater to be used for the fabrication of the semiconductor integratedcircuit device according to the one embodiment of the present invention;

[0107]FIG. 17 is a schematic diagram illustrating ion adsorption by anion exchange resin as shown in FIG. 16;

[0108]FIG. 18 is a schematic diagram of one example of a cleaning anddrafting apparatus to be used for the fabrication of the semiconductorintegrated circuit device according to the one embodiment of the presentinvention;

[0109]FIG. 19 is a schematic diagram of a dilute hydrofluoric acidpreparing apparatus for preparing dilute hydrofluoric acid to be fed tothe cleaning and drafting apparatus shown in FIG. 18;

[0110]FIG. 20 is a schematic diagram of one example of a wet etchingapparatus to be used for the fabrication of the semiconductor integratedcircuit device according to the one embodiment of the present invention;

[0111]FIG. 21 is a schematic diagram of one example of a cleaning anddrafting apparatus to be used for the fabrication of the semiconductorintegrated circuit device according to the one embodiment of the presentinvention;

[0112]FIG. 22 is a fragmentary cross-sectional view of the semiconductorintegrated circuit device during the fabrication step following the stepof FIG. 3;

[0113]FIG. 23 is a fragmentary cross-sectional view illustrating theshape of the interface between the semiconductor substrate and the gateinsulating film formed thereover after cleaning with ultrapure waterhaving ionized amines mixed therein;

[0114]FIG. 24 is a fragmentary cross-sectional view illustrating theshape of the interface between the semiconductor substrate and the gateinsulating film formed thereover after cleaning with ultrapure waterfree of ionized amines;

[0115]FIG. 25 is a schematic diagram illustrating a method of measuringthe breakdown voltage of the gate insulating film of MISFET of thesemiconductor integrated circuit device according to the one embodimentof the present invention;

[0116]FIG. 26 is a schematic diagram illustrating the results ofmeasurement of the breakdown voltage of the gate insulating film whenthe semiconductor substrate is cleaned with ultrapure water preparedjust after replacement of the UF of the UF equipment with a new one;

[0117]FIG. 27 is a schematic diagram illustrating the results ofmeasurement of the breakdown voltage of the gate insulating film whenthe semiconductor substrate is cleaned with ultrapure water preparedjust after replacement, with new ones, of an ion exchange resin typeanion removing filter and an ion exchange resin type cation removingfilter, each included in the system for preparation of ultrapure waterto be used for the fabrication of the semiconductor integrated circuitdevice according to the one embodiment of the present invention;

[0118]FIG. 28 is a schematic diagram illustrating the results ofmeasurement of the breakdown voltage of the gate insulating film whenthe semiconductor substrate is cleaned with ultrapure water preparedusing a UF of the UF equipment which has been used for a long time;

[0119]FIG. 29 is a schematic diagram illustrating the results ofmeasurement of the breakdown voltage of the gate insulating film whenthe semiconductor substrate is cleaned with ultrapure water preparedusing UF equipment having a UF replaced with a new one and having a mixdeminer disposed downstream of the equipment;

[0120]FIG. 30 is a schematic diagram illustrating the results ofmeasurement of the breakdown voltage of the gate insulating film whenthe semiconductor substrate is cleaned with ultrapure water preparedusing UF equipment having a UF replaced with a new one and having,downstream of the equipment, an ion filter with a membrane film;

[0121]FIG. 31 is a schematic diagram illustrating the relationshipbetween the amount of ionized amines attached to the semiconductorsubstrate by cleaning with ultrapure water and the existence or absenceof a defective gate insulating film;

[0122]FIG. 32 is a schematic diagram illustrating the relationshipbetween the cleaning date of the semiconductor substrate with ultrapurewater and percent of defective gate insulating films;

[0123]FIG. 33 is a fragmentary cross-sectional view of the semiconductorintegrated circuit device during the fabrication step following the stepof FIG. 22;

[0124]FIG. 34 is a fragmentary cross-sectional view of the semiconductorintegrated circuit device during the fabrication step following the stepof FIG. 33;

[0125]FIG. 35 is a fragmentary cross-sectional view of the semiconductorintegrated circuit device during the fabrication step following the stepof FIG. 34;

[0126]FIG. 36 is a fragmentary cross-sectional view of the semiconductorintegrated circuit device during the fabrication step following the stepof FIG. 35;

[0127]FIG. 37 is a fragmentary cross-sectional view of the semiconductorintegrated circuit device during the fabrication step following the stepof FIG. 36;

[0128]FIG. 38 is a fragmentary cross-sectional view of the semiconductorintegrated circuit device during the fabrication step following the stepof FIG. 39;

[0129]FIG. 39 is a fragmentary cross-sectional view of the semiconductorintegrated circuit device during the fabrication step following the stepof FIG. 38; and

[0130]FIG. 40 is a fragmentary cross-sectional view of the semiconductorintegrated circuit device during the fabrication step following the stepof FIG. 39.

DETAILED DESCRIPTION OF THE INVENTION

[0131] Prior to a detailed description of the present invention, themeanings of some terms used in this application will be explained below.

[0132] The term “wafer” means a single crystalline Si substrate(generally, having a nearly flat and circular shape), a sapphiresubstrate, a glass substrate or any other insulating, semi-insulating orsemiconductor substrate and a composite substrate thereof of the typeused for fabricating semiconductor integrated circuit devices. Further,the term “semiconductor integrated circuit device” as used herein meansnot only those devices fabricated on a semiconductor or insulatingsubstrate, such as a silicon wafer or sapphire substrate, but also thosedevices fabricated on another insulating substrate, such as glass, forexample, TFT (Thin-Film-Transistor) or STN (Super-Twisted-Nematic)liquid crystals, unless otherwise specifically indicated.

[0133] The term “device surface” means a main surface of a substrate onwhich device patterns corresponding to a plurality of chip regions areformed by lithography.

[0134] The term “resist pattern” means a film pattern obtained bypatterning a photosensitive resin film (resist film) byphotolithography. This pattern includes a simple resist film free ofopenings at such a portion.

[0135] The term “UF equipment” (Ultrafiltration Equipment) meanspressure filtration equipment for separating molecules according totheir size through use of an ultra filter (UF). In this equipment,separation is carried out at a molecular cutoff range of about thousandsto hundreds of thousands. The term “ultra filter” embraces a hollowfiber type ultra filter and a spiral type ultra filter.

[0136] The term “ion exchange resin” means a synthetic resin having acapacity of adsorbing thereto ions existing in water, thereby removingthem from the water. It can be classified into two types, that is, acation exchange resin for adsorbing and removing cations (Na⁺, Ca²⁺,Mg²⁺, etc.) and an anion exchange resin for adsorbing and removinganions (Cl⁻, SO₄ ²⁻, SiO₂, etc.). The term “ion exchange resin type ionremoving filter” embraces a cation removing filter for removing cations,an anion removing filter for removing anions and a mixed ion removingfilter for removing both cations and anions.

[0137] The term “RO unit” (Reverse Osmosis unit) means an apparatus forremoving ions, organic matter, fine particles and living bacteria inwater through use of an RO film, which is a filter membrane to whichreverse osmosis has been applied.

[0138] The term “vacuum degasifier” means an apparatus for sprayingwater in a vacuum atmosphere, thereby removing a dissolved gas in water.

[0139] The term “indifferent water” means water which will serve as araw material for obtaining high purity water to be used for thefabrication of a semiconductor integrated circuit device. River water,ground water (including well water) or the like is employed for thispurpose.

[0140] The term “primary pure water” means high purity water from whichalmost all of the impurities, such as ions, fine particles,microorganisms and organic matter, have been removed from treatmentwater (indifferent water).

[0141] The term “ultrapure water” means water which is obtained byremoving a trace of impurities, such as fine particles, living bacteria,TOC (total organic carbon), ions and dissolved oxygen remaining inprimary water, thereby having a markedly high purity, and which is to beused, for example, for the cleaning of a wafer.

[0142] The term “primary pure water unit” means one of a unitconstituting an ultrapure water preparing system. It is formed of areverse osmosis unit, an ion exchanging apparatus and a degasifier, andit prepares primary pure water by removing almost all of the impurities,such as fine particles, ions, microorganisms and organic matters, fromwater passing through a pretreatment apparatus.

[0143] The term “pretreatment system” means a system includingapparatuses for removing colloidal matter, particulate matter andbacteria from raw water by physical and chemical treatments prior to thefeeding of the raw water to a primary pure water unit.

[0144] The term “subsystem” means a system which is disposed in thevicinity of a point of use and prepares ultrapure water by using, as rawwater, primary pure water. It comprises a UV sterilizer, a cartridgepolisher and a pressure filter.

[0145] The term “ultrapure water preparing system” means a system forpreparing high purity water by separating impurities from raw water,such as tap water, industrial water, well water or river water, throughuse of an ion exchange resin membrane or a filter membrane, therebypurifying it. The system comprises a pretreatment unit, a primary purewater unit and a subsystem.

[0146] The term “point of use” means a site at which ultrapure water fedfrom a subsystem is taken out for the purpose of wafer cleaning andprovided for use.

[0147] The term “TOC (total organic carbon)” means an organic carboncontained in ultrapure water, and it embraces that material producedfrom raw water (natural water or recovered water) or that has escapedfrom the members being used, such as an ion exchange resin or pipe.

[0148] The term “ultrafiltration membrane” means a plastic porousthin-film filter having numerous uniform pores, and which is made ofcellulose nitrate, cellulose acetate, acetyl cellulose, nitrocellulose,nylon, Teflon, polyvinyl chloride or ethylene tetrafluoride resin.

[0149] The term “new” means an apparatus or member which has not beenused, and it also embraces one that has been used for a predeterminedterm. With regards to the UF referred to in the below-describedembodiment, this predetermined term corresponds to the term untildischarge of ionized amine outside the UF equipment terminates in thecase where the UF is made of an amine-containing material. Thispredetermined term varies, depending on the specification of the UF orthe amount of water fed to the UF. In the below-described embodiment,the predetermined term is about 1 month, preferably about 2 months, morepreferably about 3 months, after its use is started.

[0150] In the below-described embodiment, when reference is made to anumber of elements (including the number, value, amount and range), thenumber of elements is not limited to a specific number, but can begreater than or less than the specific number, unless otherwisespecifically indicated, or in the case where it is principally apparentthat the number is limited to the specific number.

[0151] Moreover in the below-described embodiment, it is needless to saythat the constituting elements (including element steps) are not alwaysessential unless otherwise specifically indicated or in the case whereit is principally apparent that they are essential.

[0152] Similarly, in the below-described embodiment, when a reference ismade to the shape or positional relationship of the constitutingelements, that which is substantially analogous or similar to it is alsoembraced, unless otherwise specifically indicated, or in the case whereit is utterly different in principle. This also applies to theabove-described value and range.

[0153] In all the drawings for describing the below-describedembodiment, members having a like function will be identified by likereference numerals and overlapping descriptions thereof will be omitted

[0154] In the below-described embodiments, MISFET (Metal InsulatorSemiconductor Field Effect Transistor) representing an electric fieldtransistor will be abbreviated as MIS, while a p-channel type MISFET andan n-channel type MISFET will be abbreviated as pMIS and nMIS,respectively.

[0155] The embodiments of the present invention will hereinafter bedescribed specifically based on the accompanying drawings.

[0156] In this embodiment, the present invention is applied to a methodof fabrication of a flash memory (semiconductor integrated circuitdevice). This method of fabrication of a flash memory will be describednext in the order of the steps thereof with reference to FIGS. 1 to 41.

[0157] As illustrated in FIG. 1, a semiconductor substrate(semiconductor integrated circuit wafer) 1 on which the flash memory ofthis embodiment is to be formed has, for example, a region 1A in which a5V type nMIS is formed, a region 1B in which a 5V type pMIS is formed, aregion 1C in which a MIS which is to be a memory cell of a flash memoryis formed, a region 1D in which a high breakdown-voltage one-side offsetnMIS is formed, a region 1E2 in which a high breakdown-voltage loadingnMIS is formed and a region 1F in which a high breakdown-voltageone-side offset pMIS is formed.

[0158] First, the semiconductor substrate 1 made of p type singlecrystal silicon Si is cleaned with dilute hydrofluoric acid (HF) andultrapure water, followed by oxidizing treatment on the surface of thesubstrate to form a silicon oxide film 2A thereover. After deposition ofa silicon nitride film (not illustrated) over the silicon oxide film 2A,the silicon nitride film is etched to selectively leave the siliconnitride film over the silicon oxide film 2A.

[0159] Using the resulting silicon nitride film as a mask, an impurity(for example, P (phosphorus)) having an n type conductivity isintroduced into the semiconductor substrate 1 by ion implantation. Afterselectively thickening, by oxidizing treatment, a portion of the siliconoxide film 2A in a region having no silicon nitride film formedthereover, the silicon nitride film is removed using, for example, hotphosphoric acid. The semiconductor substrate 1 is then cleaned withNH₄OH (ammonium hydroxide)/H₂O₂ (hydrogen peroxide)/H₂O, dilutehydrofluoric acid and ultrapure water. The substrate 1 is heat treatedto diffuse the above-described impurity, whereby an n type isolationregion NiSO is formed.

[0160] As illustrated in FIG. 2, after cleaning the semiconductorsubstrate 1 with dilute hydrofluoric acid and ultrapure water, oxidizingtreatment is conducted on the surface of the substrate to form a siliconoxide film 2 thereover. Using a photoresist film (not illustrated)patterned by photolithography as a mask, an impurity (for example, P)having an n type conductivity is introduced into the semiconductorsubstrate 1 by ion implantation. After removal of the photoresist film,using another photoresist film (not illustrated) patterned byphotolithography as a mask, an impurity (for example, BF₂ (borondifluoride) having a p type conductivity is introduced into thesemiconductor substrate 1 by ion implantation. The semiconductorsubstrate 1 is then cleaned with NH₄OH/H₂O₂/H₂O, hydrofluoric acid andultrapure water, followed by heat treatment to diffuse these impurities,whereby an n type well 3 and a p type well 4 are formed.

[0161] As illustrated in FIG. 3, the surface of the semiconductorsubstrate 1 is oxidized to form a silicon oxide film (not illustrated)thereover. After deposition of a silicon nitride film (not illustrated)over the silicon oxide film, the silicon nitride film is etched with aphotoresist film (not illustrated) as a mask to selectively leave thesilicon nitride film over the silicon oxide film. The photoresist filmis removed. The semiconductor substrate 1 is then cleaned withNH₄OH/H₂O₂/H₂O, followed by further cleaning with HCl/H₂O₂/H₂O. By aselective oxidization method, a field insulating film 6 for elementisolation is formed over the surface of the semiconductor substrate 1.

[0162] Using a photoresist film patterned by photolithography as a mask,an impurity (for example, BF₂) having a p type conductivity isintroduced by ion implantation. The impurity is diffused by heattreatment, whereby a p type channel stopper region 7 is formed. Thesilicon nitride film remaining on the semiconductor substrate 1 is thenremoved using, for example, hot phosphoric acid.

[0163] The semiconductor substrate 1 is then cleaned with dilutehydrofluoric acid and ultrapure water. The ultrapure water used in thisEmbodiment is prepared by a system as illustrated in FIGS. 4 and 5. FIG.4 is a schematic diagram illustrating the outline of the ultrapure waterpreparing system of this Embodiment, while FIG. 5 is a schematic diagramillustrating one example of the details of the ultrapure water preparingsystem illustrated in FIG. 4. A technique relating to such a ultrapurewater preparing system is also described in Japanese Patent ApplicationNo. 2001-314813 by the present inventors.

[0164] As illustrated in FIGS. 4 and 5, by the pretreatment system(primary purifying system) PTS, groundwater (indifferent water (firstraw material water) which will hereinafter be called “raw water”) pumpedup from a well is subjected to chemical and physical treatments toremove colloidal matter (first foreign matter), particulate matter(first foreign matter) and bacteria (first foreign matter) from the rawwater. By use of an RO unit (primary purifying system) RO1, fineparticles (first foreign matter), organic matter (first foreign matter),bacteria (first foreign matter) and high molecular ions (first foreignmatter) are removed from the raw water. By use of an ion exchange resintype cation removing filter (primary purifying system) CED1, cations(first foreign matter) are removed from the raw water, followed byremoval of a dissolved gas in the raw water by a vacuum degasifier (VD).By an ion exchange resin type anion removing filter (primary purifyingsystem) AED1, anions (first foreign matter) are removed from the rawwater. After removal of cations (first foreign matter) from the rawwater by an ion exchange resin type cation removing filter (primarypurifying system), anions are removed from the raw water by an ionexchange resin type anion removing filter (primary purifying system)AED2. Downstream thereof, an RO unit RO2 (not illustrated in FIG. 5) maybe disposed to remove, from the raw water, fine particles generated fromthe anion and cation removing filters. Through the above-describedsteps, primary pure water can be prepared from the raw water. Theprimary pure water system (pretreatment system) described here is madeup of units used for preparing primary pure water from the raw water.

[0165] The primary pure water (second raw material water) thus preparedis then fed to an intermediate storage tank (secondary purifying system)MIDT, followed by delivery to a heat exchanger (secondary purifyingsystem) HEXC by a pump (secondary purifying system) PUMP. While theprimary pure water is kept at a fixed temperature by means of the heatexchanger HEXC, it is fed to an UV sterilizer (secondary purifyingsystem) UV01 or a low-pressure UV oxidizer (secondary purifying system)UVO2, in which the primary pure water is oxidized or sterilized byexposure to UV rays. The primary pure water sterilized by the UVsterilizer UVO1 is caused to pass through an ion exchange resin typemixed ion removing filter (secondary purifying system) MED to removecations and anions, and it then delivered to UF equipment (firstequipment) UFE. Fine particles and the like, which cannot be removed bythe RO unit and ion removing filter, can be removed by the UF equipmentUFE, making it possible to prepare ultrapure water (secondary purewater) to be used for the fabrication of the semiconductor integratedcircuit device of this Embodiment and to feed the thus preparedultrapure water to a point of use USEP. The secondary pure water system(subsystem (secondary pure water circulating system)) is formed of eachequipment for preparing ultrapure water from primary pure water andpoint of use USEP.

[0166] Of the ultrapure water sent to the point of use USEP, a portionof it which has not been used up at the point of use USEP can bereturned to the intermediate storage tank MIDT for recycling. Of theultrapure water used at the point of use USEP (which water willhereinafter be called “wastewater”), that which is re-usable asultrapure water is subjected to ion exchange to remove cations andanions. The wastewater is then subjected to sterilizing treatment andtreatment for removal of impurities, such as fine particles, organicmatter, bacteria and high molecular ions, by using an RO unit RO3 havinga sterilizing capacity by exposure to ultraviolet rays and afine-particle removing capacity through use of an RO membrane. Aftervarious treatments as described above, the wastewater, together with theraw material treated by the RO unit RO1, is sent to the cation removingfilter CED1. After these steps, a portion of the wastewater becomesre-usable as ultrapure water.

[0167]FIG. 6 is a schematic diagram of a UF module of the UF equipmentUFE illustrated in FIGS. 4 and 5. FIG. 7 is a cross-sectional view takenalong a line A-A of FIG. 6. The UF module in this Embodiment is made bydisposing, in a body KOT, a plurality of capillary hollow fibermembranes TYM that are formed from a polysulfone membrane or polyimidemembrane, bonding these plurality of hollow fiber membranes TYM at endportions thereof by hot welding, and by this hot welding, adhering thesehollow fiber membranes TYM to the body. As illustrated in FIG. 8, thehollow fiber membranes are each made of a polysulfone membrane orpolyimide membrane so that water, ion molecules and low molecules canpenetrate inside of the hollow fiber membranes TYM, but high moleculescannot. Since the plurality of hollow fiber membranes TYM are hot weldedto each other at end portions thereof in the body KOT and the hollowfiber membranes TYM are adhered to the body, there is discharged fromthe UF module only primary pure water which has penetrated inside of thehollow fiber membranes TYM, and thereby it is deprived of highmolecules, that is, ultrapure water.

[0168] When the plurality of hollow fiber membranes TYM are bonded toeach other at end portions thereof by an adhesive containing an epoxyresin as its raw material, the adhesive typically contains an amine, anda portion of this amine exists in an ionized form. In this Embodiment,on the other hand, the plurality of hollow fiber membranes TYM are hotwelded at end portions thereof so that the adhered portions do notcontain an amine. Therefore, use of the UF module of this Embodimentmakes it possible to prevent the discharge of an ionized amine whichwill otherwise occur when primary pure water is fed to the UF module andthe ionized amine is hydrophilized and then, discharged as a mixturewith ultrapure water. Even if ultrapure water prepared by the ultrapurewater preparing system according to this Embodiment is used for acleaning step of the semiconductor substrate 1 just before the formationof a gate oxide film of the MISFET, which will be a memory cell of aflash memory, it is possible to prevent an inconvenience, such as theformation of an unevenness on the interface between a gate oxide filmand the semiconductor substrate 1 after formation of the gate oxidefilm, which will otherwise be caused by etching of the semiconductorsubstrate by the ionized amine. This results in the prevention oflowering in the breakdown voltage of the gate oxide film, thereby makingit possible to prevent deterioration in the write characteristics anderase characteristics. Lowering in the breakdown voltage of the gateoxide film can be prevented so that even in a MISFET other than a memorycell, the smooth flow of electric current between the source and drainis not disturbed. In this Embodiment, the plurality of hollow fibermembranes TYM are bonded to each other by hot welding, but hot weldingmay be replaced with bonding via an amine-free urethane material.

[0169] Downstream of the UF equipment UFE (refer to FIGS. 4 and 5), anion filter (first filter), having a membrane film MBF in a circularsheet form, may be disposed as illustrated in FIG. 9. The ultrapurewater passing through the UF equipment UFE is supplied to its ion filterand then, enters into the membrane film MBF from a membrane hole MBH ofthe membrane film MBF. As illustrated in FIG. 10, an ion exchangeradical IER has been formed in the membrane hole MBH. Ions in theultrapure water are adsorbed to this ion exchange radical IER and thuscan be removed. In other words, even if a plurality of hollow fibermembranes TYM disposed in the UF module of the UF equipment UFE (referto FIGS. 4 and 5) are bonded to each other at end portions thereof by anamine-containing adhesive (for example, an epoxy resin) and the ionizedamine is discharged together with ultrapure water, it can be removedfrom the ultrapure water by causing the water to pass through theabove-described ion filter.

[0170] As illustrated in FIG. 11, it is possible to omit the anionremoving filter AED3 and mixed ion removing filter MED from theultrapure preparing system of this Embodiment, as illustrated in FIGS. 4and 5, and to dispose an ion filter, as illustrated in FIG. 9,downstream of the UF equipment. In FIG. 11, the heat exchanger HEXS isnot illustrated. When the system does not include these filters, an ionfilter IFA having an ion exchange radical capable of adsorbing theretoanions and an ion filter IFC having an ion exchange radical capable ofadsorbing thereto cations are disposed as the ion filter. Without usingthe anion removing filter AED3 and mixed ion removing filter MED, anionsand cations can be removed from the primary pure water by the ion filterIFA and ion filter IFC. Moreover, even when the ionized amine runs offfrom the UF module, it can be removed by the ion filters IFA and IFC. Insuch a ultrapure water preparing system of this Embodiment, the anionremoving filter AED3 and mixed ion removing filter MED can be omitted,which contributes to simplification of this system. This makes itpossible to facilitate the maintenance of the ultrapure water preparingsystem of this Embodiment.

[0171] As illustrated in FIG. 12, the anion removing filter AED3 andmixed ion removing filter MED in the ultrapure water preparing system ofthis Embodiment, as illustrated in FIGS. 4 and 5, may be replaced withthe above-described ion filter (second filter) IFA and ion filter(second filter) IFC. In FIG. 12, the heat exchanger HEXC is notillustrated. Since the ion exchange resin constituting the anionremoving filter AED3 and mixed ion removing filter MED contains anamine, there is a possibility of ionized amine leaking from the anionremoving filter AED3 and mixed ion removing filter MED when primary purewater is caused to pass through these filters. The test made by thepresent inventors has revealed that ionized amine is leaked from theanion removing filter AED3 and mixed ion removing filter MED, and theleakage amount from the anion removing filter AED3 is greater. It istherefore possible to be free from an inconvenience, such as caused by aleakage of ionized amine, when the anion removing filter AED3 and mixedion removing filter MED are replaced with the ion filters IFA and IFC.

[0172] As illustrated in FIG. 13, the ion filter IFC may be installed inthe pipe line (pathway) PL for delivering ultrapure water to the pointof use USED from the UF equipment UFE. The point of use USEP embracesnot only cleaning and drafting equipment (first wet treating equipment)to be used for the cleaning (first wet treatment) of the semiconductorsubstrate 1, but also chemical-solution preparing equipment (first wettreating equipment) in which a chemical solution, such as dilutehydrofluoric acid, is prepared using ultrapure water. Ionized amine is acation so that installment of the ion filter IFC in the pipe line PLmakes it possible to remove, by use of the filter IFC, ionized aminefrom ultrapure water to be fed to the point of use USEP, even if ionizedamine flows out from the UF equipment UFE as a mixture in ultrapurewater. In this Embodiment, the ion filter IFC is installed in the pipeline PL. Instead of the ion filter IFC, a mixed ion removing filter maybe used for the removal of ionized amine from ultrapure water.

[0173] The UF equipment UFE is made of a plurality of UF modules UFM, asillustrated in FIG. 14. Similar to the UF modules as described withreference to FIG. 6, these UF modules UFM have, disposed in the bodythereof, a plurality of capillary hollow fiber membranes made of apolysulfone membrane or polyimide membrane. When the plurality of hollowfiber membranes are bundled using an amine-containing adhesive, ionizedamine presumably comes to be mixed in ultrapure water discharged fromthe UF modules UFM. Therefore, in this Embodiment, the above-describedion filter IFC is disposed upstream of each of the UF modules UFM. Thismakes it possible to remove ionized amine by use of the ion filter IFCeven if ionized amine is mixed in the ultrapure water discharged fromthe UF modules UFM. Upon disposal, the capacity for allowing the passageof water is set to be greater in the ion filter IFC than in the UFmodule UFM. When the ion filter IFC is inferior with regard to thiscapacity relative to the UF module UFM, a plurality of the ion filtersIFC are disposed per UF module UFM, so that the total capacity of theplurality of ion filters IFC would exceed that of one UF module UFM.

[0174] When a plurality of hollow fiber membranes are bundled by anamine-containing adhesive, as in the above-described UF modules UFM, theamount of ionized amine is small relative to the whole amine amount. Ofthe whole amine amount, only ionized amine is hydrophilized and flowsout from the UF modules UFM, passing through the hollow fiber membranes.Most of the amine existing in the ionized form is discharged from the UFmodules together with ultrapure water after an elapse of a predeterminedterm after disposal of new UF modules in the UF equipment UFE, whichterm varies depending on the amount of water caused to pass through theUF modules. An area for installing new UF modules UFMN is established inthe UF equipment UFE, as illustrated in FIG. 15. To new UF modules UFMNinstalled in this area, as well as to the other UF modules UFM, primarypure water, which has passed through the anion removing filter AED3 andmixed ion removing filter MED, is fed. The primary pure water that isfed to the new UF modules UFMN is discharged from the new UF modulesUFMN as ultrapure water containing ionized amine existing in the new UFmodules UFMN, it is fed to the upstream side of the anion removingfilter AED3 and mixed ion removing filter MED, and then it unites withthe primary pure water upstream thereof. The ultrapure water, togetherwith the primary pure water, is then fed to the anion removing filterAED3 and mixed ion removing filter MED. The anion removing filter AED3and mixed ion removing filter MED used here each has, in the body KOT1thereof, a plurality of ion exchange resins IEJ disposed as illustratedin FIG. 16. As illustrated in FIG. 17, the ion exchange resins IEF eachhas an ion exchange radical IER1, which adsorbs thereto ions in theprimary pure water fed to the body KOT1. Ionized amine contained in theultrapure water is a cation so that it can be adsorbed to and removed bythe mixed ion removing filter MED. The ultrapure water from whichionized amine has been removed is fed again to the UF equipment UFEtogether with the primary pure water. The above-described steps are thenrepeated. By these steps, new UF modules UFMN can be cleaned to removethe ionized amine existing therein, whereby primary pure water which isused for the removal of ionized amine can be provided for recycling usewithout being discarded. The test made by the present inventors hasrevealed that, when a column having a diameter of about 106 mm and aheight of 1150 mm was used as a new UF module UFMN, run-off of ionizedamine from the new UF module UFMN stopped about two or three months(preferably about 3 months) after about 3 m³ per hour of the primarypure water was caused to pass through the new UF module UFMN. Such a newUF module UFMN, which becomes free from leakage of ionized amine aftersuch a step, can be used as a substitute for an old UF module UFM. Thenumber of such new UF modules UFMN to be disposed of must be equal orgreater than that of the UF modules which are worn and need replacement.The number of new modules can be set freely depending on whether the oldUF modules UFM are replaced wholly or partially.

[0175] Alternatively, new UF modules UFMN, as described above, may beinstalled in a pathway (refer to FIGS. 4 and 5) for returning, to anintermediate storage tank MIDT, a nonused portion of ultrapure water atthe point of use USEP. Ultrapure water fed to the new UF module UFMN isdischarged therefrom as ultrapure water containing the ionized amineexisting in the new UF module UFMN. This ionized-amine-containingultrapure water is sent to the intermediate storage tank MIDT (refer toFIGS. 4 and 5), and there it unites with primary pure water. The ionizedamine can be removed when the primary pure water passes through themixed ion removing filter MED (refer to FIGS. 4 and 5). The ultrapurewater from which ionized amine has been removed is fed again to the UFequipment UFE together with the primary water. The above-described stepsare then repeated. By such steps, ionized amine existing in the new UFmodule UFMN can be removed. Moreover, ultrapure water used for theremoval of ionized amine can be provided for recycling without beingdiscarded.

[0176] As described above, the ion exchange resin IEJ (refer to FIGS. 16and 17) constituting the anion removing filter AED3 and mixed ionremoving filter MED contains an amine. The amine in the ion exchangeresin does not contain so much ionized amine. As in the UF module UFM,the ionized amine is hydrophilized and inevitably flows out from theanion removing filter AED3 and mixed ion removing filter MED. It istherefore possible to remove ionized amine contained in the ion exchangeresin IEJ by disposing new anion removing filters AED3 and mixed ionremoving filters MED in an area similar to the area in which the new UFmodules UFMN are disposed. The ionized amine contained in the ionexchange resin IEJ may be removed, as in the case of the new UF modulesUFMN, by disposing new anion removing filters AED3 and mixed ionremoving filters MED in a pathway (refer to FIGS. 4 and 5) for returninga nonused portion of the ultrapure water at the point of use USEP to anintermediate storage tank MIDT.

[0177] When the ultrapure water prepared through the above-describedsteps is used in a cleaning step of the semiconductor substrate 1, fromwhich a silicon nitride film used for the formation of theabove-described field insulating film 6 (refer to FIG. 3) has beenremoved, a cleaning and drafting apparatus, as illustrated in FIG. 18,can be used. The ultrapure water prepared by the ultrapure waterpreparing system of this Embodiment, which has been described withreference to FIGS. 4 to 17, is fed to each of a treatment tank SC1 andpure water tanks QDR1, QDR2, OF1 and OF2, which are points of use USEDof ultrapure water (refer to FIGS. 4 and 5). As described above withreference to FIG. 13, an ion filter IFC having an ion exchange radicalcapable of adsorbing thereto cations or a mixed ion removing filter MEDmay be installed in respective pipe lines for feeding ultrapure water tothe treatment tank SC1 and pure water tanks QDR1, QDR2, OF1 and OF2. Thetreatment tank SC1 is fed with H₂O₂ and NH₄OH, while the treatment tankHF is fed with dilute hydrofluoric acid prepared using the ultrapurewater of this Embodiment. The semiconductor substrate 1 is cleaned, asdescribed below, by such a cleaning and drafting apparatus. First,cleaning with NH₄OH/H₂O₂/H₂O is conducted in the treatment tank SC1,followed by cleaning with ultrapure water in the pure water tanks QDR1and OF1. After cleaning with dilute hydrofluoric acid in the treatmenttank HF, cleaning with pure water is conducted in the pure water tanksQDR2 and OF2. The semiconductor substrate 1 is then dried by IPA(isopropyl alcohol) vapor drying method, by which the step of cleaningthe semiconductor substrate 1 using the cleaning and drafting apparatusillustrated in FIG. 18 is completed. When the cleaning and draftingapparatus as illustrated in FIG. 18 is applied to another cleaning step,which does not need the treatment in the treatment tank SC1 and purewater tanks QDR1 and OF1, the cleaning step may be started from thetreatment in the treatment tank HF.

[0178]FIG. 19 is a schematic view of a dilute hydrofluoric acidpreparing apparatus. This dilute hydrofluoric acid preparing apparatusis one of the points of use USEP of ultrapure water (refer to FIGS. 4and 5). The ultrapure water prepared by the ultrapure water preparingsystem of this Embodiment, as described with reference to FIGS. 4 to 17,is first fed in a predetermined amount to a pure water weighing tankTANK 1. As described above with reference to FIG. 13, an ion filter IFChaving an ion exchange radical capable of adsorbing thereto cations or amixed ion removing filter MED is installed in the pipe line for feedingultrapure water to the pure water weighing tank TANK 1. Undilutedhydrofluoric acid fed from a hydrofluoric acid canister CAN1 to anundiluted hydrofluoric acid tank TANK 2 is weighed by being transferredfrom the undiluted hydrofluoric acid tank TANK2 to a hydrofluoric acidweighing tank TANK 3. From the pure water weighting tank TANK 1 and thehydrofluoric acid weighing tank TANK 3, ultrapure water and undilutedhydrofluoric acid are then fed respectively to a blending tank TANK4, inwhich ultrapure water and the undiluted hydrofluoric acid are blended ata predetermined ratio to prepare dilute hydrofluoric acid. In thisEmbodiment, an example consists of an about 1:99 or 1:19 mixture ofundiluted hydrofluoric acid and ultrapure water. The dilute hydrofluoricacid is then transferred from the blending tank TANK4 to a feeding tankTANK5, whereby it can be provided for a cleaning and drafting apparatus.

[0179] After removal of the silicon nitride film used for the formationof the field insulating film 6 (refer to FIG. 3) and cleaning of thesemiconductor substrate 1, the surface thereof is oxidized to formthereover a gate insulating film 8 having a film thickness of about 20nm. By wet etching with a photoresist film (not illustrated) patternedby photolithography, the gate insulating film 9 in a region 1C isselectively removed. In this Embodiment, wet etching can be carried outby a wet etching apparatus (refer to FIG. 20) which uses ultrapure waterprepared by the ultrapure water preparing system of this Embodiment, asdescribed above with reference to FIGS. 4 to 17. The ultrapure water isfed to each of the pure water tanks QDR3, OF3 and OF4, which are pointsof use USEP (refer to FIGS. 4 and 5) of the ultrapure water. Asdescribed above with reference to FIG. 13, an ion filter IFC having anion exchange radical capable of adsorbing thereto cations or a mixed ionremoving filter MED may be installed in each of the pipe lines forfeeding the pure water tanks QDR3, OF3 and OF4 with ultrapure water. Anetching tank ETCH contains an etching solution for etching of thesilicon oxide film. In such a wet etching step of the gate insulatingfilm 8 by the wet etching apparatus, the gate insulating film 8 is wetetched by immersing the semiconductor substrate 1 in the etching tankETCH. After cleaning the semiconductor substrate 1 using ultrapure waterin the pure water tanks OF3 and OF4, the semiconductor substrate 1 isdried by spin drying, whereby the wet etching step of the gateinsulating film 8 performed by the wet etching apparatus illustrated inFIG. 20 is completed.

[0180] After removal of the photoresist film, the semiconductorsubstrate 1 is cleaned, for example, by a cleaning and draftingapparatus, as illustrated in FIG. 21. The ultrapure water prepared bythe ultrapure water preparing system of this Embodiment, as describedwith reference to FIGS. 4 to 17, is fed to each of the treatment tanksSC2 and SC3, and the pure water tanks QDR3, QDR4, OF5 and OF6 which areeach a point of use USEP of the ultrapure water (refer to FIGS. 4 and5). As described above with reference to FIG. 13, an ion filter IFChaving an ion exchange radical capable of adsorbing thereto cations or amixed ion removing filter MED may be installed in respective pipe linesfor feeding the treatment tanks SC2 and SC3, and pure water tanks QDR3,QDR4, OF5 and OF6. The treatment tank SC2 is fed with H₂O₂ and NH₄OH,while the treatment tank SC3 is fed with H₂O₂ and HC1 (hydrochloricacid). Cleaning of the semiconductor substrate 1 by such a cleaning anddrafting apparatus is carried out in the following manner. First,cleaning with NH₄OH/H₂O₂/H₂O is conducted in the treatment tank SC2,followed by cleaning with the ultrapure water in the pure water tanksQDR3 and OF5. After cleaning with HCl/H₂O₂/H₂O in the treatment tankSC3, cleaning with ultrapure water is conducted in the pure water tanksQDR4 and OF6. The semiconductor substrate 1 is dried by use of an IPAvapor drying method, whereby the cleaning of the semiconductor substrate1 by the cleaning and drafting apparatus as illustrated in FIG. 21 iscompleted.

[0181] As illustrated in FIG. 22, the surface of the semiconductorsubstrate 1 is oxidized to form a gate insulating film (tunnel oxidefilm) 9 having a film thickness of about 10 nm over the surface of the ptype well 4 in a region 1C. The gate insulating film 9 may have a filmthickness not greater than 10 nm, for example, about 5 nm.

[0182] By CVD, a polycrystalline Si film (first conductive film) 10 ofabout 200 nm thick is deposited over the main surface (device surface)of the semiconductor substrate 1. This polycrystalline Si film 10 may beformed by depositing amorphous Si over the semiconductor substrate 1 byCVD and then heat treating this amorphous Si to convert amorphous Si topolycrystalline Si.

[0183] After deposition of a phosphate glass film (not illustrated) overthe surface of the polycrystalline Si film 10, for example, by thecoating method, the semiconductor substrate 1 is heat treated tointroduce P into the polycrystalline Si film 10. After removal of thephosphate glass film, the polycrystalline Si film 10 is patterned byphotolithography using a photoresist film (not illustrated) as a mask.This makes it possible to leave the polycrystalline Si film 10 in theregion 1C, and to form gate electrodes 10D, 10E2 and 10F in the regions1D, 1E2 and 1F, respectively. After removal of the photoresist film thatwas used for patterning of the polycrystalline Si film 10, heattreatment at about 950° C. is conducted to form a silicon oxide film(first insulating film) 11 over the surface of the polycrystalline Sifilm 10 (including gate electrodes 10D, 10E2 and 10F).

[0184] In the cleaning of the semiconductor substrate 1 with ultrapurewater, the ultrapure water, if it contains ionized amine, inevitablyetches the Si constituting the semiconductor substrate 1. As illustratedin FIG. 23, which is an enlarged view of the region IC, the interfacebetween the gate insulating film 9 and the semiconductor substrate 1 (ptype well 4) becomes uneven. This unevenness adversely affects the shapeof a thin film formed over the gate insulating film 9 and the interfacebetween the gate insulating film 9, and polycrystalline Si film 10 orthe interface between the polycrystalline Si film 10 and silicon oxidefilm 11 sometimes becomes uneven.

[0185] By using the ultrapure water preparing system of this Embodiment,as described with reference to FIGS. 4 to 17, inclusion of ionized aminein the ultrapure water can be prevented. Therefore, use of the ultrapurewater prepared according to this Embodiment can prevent the formation ofunevenness on the interface between the gate insulating film 9 andsemiconductor substrate 1 (p type well 4) (refer to FIG. 24). This makesit possible to prevent a lowering of the breakdown voltage of the gateinsulating film so that when a MISFET, which will constitute a memorycell of a flash memory is formed in the region IC, deterioration in thewrite characteristics to the memory cell and the erase characteristicscan be prevented.

[0186] The present inventors measured the breakdown voltage of the gateinsulating film 9 in a manner as shown in FIG. 25. More specifically,the applied voltage, when an electric current of about 1×10⁻¹¹ is sentbetween the semiconductor substrate 1 and polycrystalline Si film 10,was measured by a probe. In FIG. 25, members other than thesemiconductor substrate 1, field insulating film 6, gate insulating film9 and polycrystalline Si film 10 are omitted. FIGS. 26 to 30 show theresults of measurement of the breakdown voltage of the gate insulatingfilm 9 at plural sites on the whole surface of the semiconductor wafer(semiconductor substrate 1). The gate insulating films 9 at sitesshowing a voltage less than 8V are regarded as defective because of adecline in breakdown voltage.

[0187]FIG. 26 shows the results of measurement of the breakdown voltageof the gate insulating film 9 that is formed after cleaning thesemiconductor substrate 1 with the ultrapure water which has beenprepared just after replacement of the UF modules UFM (refer to FIG. 14)of the UF equipment UFE with new ones. In FIG. 26, results are shown forthe case where the UF equipment is not equipped with the ion filter IFCillustrated in FIG. 14. As described above with reference to FIG. 14,the UF modules UFM each has, in the body thereof, a plurality of hollowfiber membranes bundled with an amine-containing adhesive. In a novel UFmodule UFM, a portion of an amine exists as ions. The ionized amine ishydrophilized and flows out from the UF module as a mixture with theultrapure water. In the cleaning of the semiconductor substrate 1 withthe ultrapure water, this ionized amine inevitably etches the Siconstituting the semiconductor substrate 1, thereby forming anunevenness on the interface between the surface and the gate insulatingfilm 9 formed thereover. It has been confirmed from the test resultsshown in FIG. 26 that this unevenness lowers the breakdown voltage ofthe gate insulating film 9.

[0188]FIG. 27 shows the results of measurement of the breakdown voltageof the gate insulating film 9 that is formed after cleaning thesemiconductor substrate 1 with the ultrapure water which has preparedjust after the replacement of the anion removing filter AED3 and mixedion removing filter MED (refer to FIGS. 4 and 5) with new ones. Similarto the results shown in FIG. 26, FIG. 27 shows the results obtained inthe case where the ion filter IFC illustrated in FIG. 14 is notinstalled. As described above with reference to FIG. 12, the ionexchange resin constituting the anion removing filter AED3 and mixed ionremoving filter MED contains amines, so that when the primary waterpasses through these filters, ionized amine runs out from them. Thisionized amine is hydrophilized and discharged from the UF equipment UFEas a mixture with the ultrapure water. Similar to the results shown inFIG. 26, this ionized amine inevitably etches the Si constituting thesemiconductor substrate 1, thereby forming an unevenness on theinterface between its surface and the gate insulating film 9 formedthereover. It has been confirmed from the test results shown in FIG. 27that this unevenness lowers the breakdown voltage of the gate insulatingfilm 9.

[0189]FIG. 28 shows the results of measurements of the breakdown voltageof the gate insulating film 9 that is formed after the cleaning of thesemiconductor substrate 1 with ultrapure water prepared using the UFmodules UFM of the UFE equipment UFE which have been used for a longtime (for example, at least about 3 months). Similar to the resultsshown in FIG. 26 or FIG. 27, FIG. 28 shows results in the case where theion filter IFC illustrated in FIG. 14 is not installed. As describedabove with reference to FIG. 15, most of the amines existing in ionizedform are discharged, together with the ultrapure water, from the UFmodules after an elapse of a predetermined term, which varies dependingon the amount of water caused to pass through the UF modules UFM. Thereis no possibility of the ionized amine flowing out from the UF modulesUFM if they have been used for a long time so that unevenness on theinterface between the semiconductor substrate 1 and the gate insulatingfilm 9, which will otherwise be formed as a result of etching, by theionized amine, of the Si constituting the semiconductor substrate 1,does not occur. It can be confirmed also from the test results shown inFIG. 28 that the gate insulating film 9 is free from a reduction in thebreakdown voltage because such an inconvenience is inhibited.

[0190]FIG. 29 shows the results of measurements of the breakdown voltageof the gate insulating film 9 that is formed after cleaning thesemiconductor substrate 1 (refer to FIG. 13) with the ultrapure waterprepared by replacing the UF modules UFM with new ones and disposing amixed ion removing filter MED downstream of the UF equipment UFE. Inthis case, the ionized amine flowing out from the new UF modules UFM canbe removed by the mixed ion removing filter MED, so that unevenness onthe interface between the semiconductor substrate 1 and the gateinsulating film 9, which will otherwise be formed as a result ofetching, by the ionized amine, of the Si constituting the semiconductorsubstrate 1, does not occur. It can be confirmed also from the testresults shown in FIG. 29 that the gate insulating film 9 is free from areduction in the breakdown voltage because such an inconvenience isinhibited.

[0191]FIG. 30 shows the results of measurement of the breakdown voltageof the gate insulating film 9 that is formed after cleaning thesemiconductor substrate 1 (refer to FIG. 13) with the ultrapure waterprepared by replacing the UF modules UFM with new ones and disposing anion filter IFC (refer to FIG. 11) downstream of the UF equipment UFE. Inthis case, the ionized amine flowing out from the new UF modules UFM canbe removed by the ion filter IFC so that unevenness on the interfacebetween the semiconductor substrate 1 and the gate insulating film 9,which will otherwise be formed as a result of etching, by the ionizedamine, of the Si constituting the semiconductor substrate 1, does notoccur. It can be confirmed also from the test results shown in FIG. 30that the gate insulating film 9 is free from a reduction in thebreakdown voltage because such an inconvenience is inhibited.

[0192]FIG. 31 illustrates the relationship, classified by specification,between the amount of ionized amine attached to the semiconductorsubstrate 1 as a result of cleaning with ultrapure water and theexistence or absence of a defective gate insulating film 9, asdetermined by the testing method illustrated in FIG. 25. At this time,the ultrapure water is fed to a cleaning and drafting apparatus (referto FIG. 18) at a rate of 15 liter/minute. The cleaning step is startedwith the treatment in the treatment tank HF. After removal of the gateinsulating film 8 that is formed in the region IC to expose the Siconstituting the semiconductor substrate 1, treatment is conducted inthe pure water tanks QDR2 and OF2. Since the amount of ionized aminemixed in the ultrapure water was only a trace, the treatment time in thepure water tank OF2 was adjusted to about 100 minutes so that the amountof ionized amine attached to the semiconductor substrate 1 is clearlydifferent among the specifications of the ultrapure water preparingsystem. The item indicated as “P test” shows the test results by thetesting method (which will hereinafter be called a “probe test”)illustrated in FIG. 25. Among the specifications of the ultrapure waterpreparing system to be tested, the specification indicated by “ReF” hasUF modules UFM of the UF equipment UFE, which modules have been used fora long period of time (for example, about three months or greater). Thespecification indicated by “new UF” has new UF modules as the modules ofthe UF equipment UFE. The specification 1 indicates UF equipment UFEinstalled with new UF modules UFM after cleaning for about 2 weeks in asimilar manner to that described above with reference to FIG. 15. Thespecification 2 indicates UF equipment UFE installed with new UF modulesafter cleaning for about 6 weeks in a similar manner to that describedabove with reference to FIG. 15. The specification 3 indicates UFequipment UFE which is installed with new UF modules and has a cationdeminer and an anion deminer disposed downstream of the UF equipment UFE(between the UF equipment UFE and point of use USEP). The specification4 indicates UF equipment UFE (FIG. 11), which is installed with new UFmodules UFM and has an ion filter IFA and an ion filter IFC disposeddownstream of the UF equipment UFE (between the UF equipment UFE andpoint of use USEP). As a result of comparison of the attached amount ofionized amine among these specifications, supposing that the attachedamount of ionized amine in ReF is 100, the amount is greater in the newUF, Specification 1, Specification 2 and Specification 3 than in ReF.According to the results of the probe test, the new UF and specification1 are judged to be defective. Although the specification 2 is judged tobe defective as a result of the probe test, its defectiveness is lighterthan that of the new UF or specification 1. From these results, theeffectiveness of the ultrapure water preparing system of thisEmbodiment, characterized in that ionized amine is removed by the UFequipment and an ion exchange resin type ion removing filter (ion filterIFA and ion filter IFC) or deminer (cation removing filter and anionremoving filter) disposed downstream of the UF equipment UFE (betweenthe UF equipment and the point of use USEP) has been confirmed, alongwith the effectiveness of the use of new UF modules UFM, as illustratedin FIG. 15, after cleaning for a predetermined term.

[0193]FIG. 32 illustrates the relationship between the percentdefectives of the gate insulating film 9 and the date on which thesemiconductor substrate 1 was cleaned with ultrapure water reckoned fromthe date on which the UF modules UFM of the UF equipment UFE arereplaced with new ones. At the time when mass production (cleaning step)of the flash memory of this Embodiment is started again afterreplacement of the UF modules UFM with new ones, a TOC content in theultrapure water, its specific resistance and the concentration ofdissolved oxygen in the ultrapure water have recovered their normalvalues, more specifically, approximately 1.0±0.2 ppb, 18.25 MΩ and20±3.0 ppb, respectively. Although the mass production is restarted whenthis TOC content, specific resistance and concentration of dissolvedoxygen become normal values, some gate insulating films 9 are defective,suggesting that these elements have no relationship with the percent ofdefective gate insulating films 9. The TOC content, specific resistanceand dissolved oxygen concentration, each of the ultrapure water, becomethe above-described values for about 1.5 days, about 0.5 day and about0.5 day after replacement of the UF modules UFM with the new ones, sothat for about three days after replacement with the UF modules UFM withnew ones, the cleaning step is not conducted even though ultrapure wateris provided. The percent of defective gate insulating films 9 increasesjust after the day of replacement of the UF modules UFM with new ones,followed by a gradual decrease day by day. This occurs because, as theprimary pure water passes through the new UF modules UFM, the ionizedamine existing in the new UF modules UFM flows out and its amountdecreases. From the above-described results, the effectiveness of thecleaning of new UF modules UFM for a predetermined term, as illustratedin FIG. 15, can be confirmed.

[0194] As illustrated in FIG. 33, a silicon nitride film 13, a siliconoxide film 14 and a silicon nitride film 15 are successively stackedover the semiconductor substrate 1. The silicon nitride films 13, 15 areformed, for example, by deposition by CVD, while the silicon oxide film14 is formed, for example, by heat treating the semiconductor substrate1. The silicon oxide films 11, 14 and silicon nitride films 13, 15 arecalled an interlayer capacitor film 16, collectively. Using aphotoresist film (not illustrated) patterned by photolithography as amask, the interlayer capacitor film 16 is dry etched to remove theinterlayer capacitor film 16 from the regions 1A, 1B.

[0195] Over the surface of the p type well 4 in the region 1A and thesurface of the n type well 3 in the region 1B, a silicon oxide film (notillustrated) is formed by oxidizing treatment. Then, into the p typewell 4 in the region 1A and n type well 3 in the region 1B, BF₂ isintroduced.

[0196] After removal of the photoresist film that is used for dryetching of the interlayer capacitor film 16, the surface of thesemiconductor substrate 1 is oxidized to form, for example, a gateinsulating film 17 of about 13.5 nm thick over the surface of the p typewell 4 in the region 1A and the surface of the n type well 3 in theregion 1B, as illustrated in FIG. 34.

[0197] Over the main surface of the semiconductor substrate 1, apolycrystalline Si film (second conductive film) 18, WSi_(x) film(second conductive film) 19 and silicon oxide film 20 are stackedsuccessively. After the deposition of the polycrystalline Si film 18, aphosphate glass film (not illustrated) may be deposited by the coatingmethod, followed by heat treatment of the semiconductor substrate 1 tointroduce P into the polycrystalline Si film 18.

[0198] As illustrated in FIG. 35, using a photoresist film (notillustrated) that has been patterned by photolithography as a mask, thesilicon oxide film 20 is patterned. After removal of the photoresistfilm, the WSi_(x) film 19 and the polycrystalline Si film 18 are dryetched using the silicon oxide film 20 as a mask. By this step, in theregions 1A and 1B, gate electrodes 29A, 29B made of the WSi_(x) film 19and the polycrystalline Si film 18 can be formed, respectively, while inthe region 1C, a control gate electrode 22, that is made of theWSi_(x film) 19 and the polycrystalline Si film 18, can be formed. Inthe regions 1E2, 1D, 1F, the interlayer capacitor film 16 is etched,while leaving the silicon nitride film 13.

[0199] As illustrated in FIG. 36, the polycrystalline Si film 10 is dryetched using the silicon oxide film 20 as a mask in the region 1C,whereby a floating gate electrode 24 can be formed. A region other thanthe region 1C is covered with the photoresist film so that exposure tothe etching atmosphere can be prevented. Here, the floating gateelectrode 24, interlayer capacitor film 16 and control gate electrode 22are called the gate electrode 25, collectively. Oxidizing treatment isthen conducted to form a thin silicon oxide film 30 on the side wallsand upper surfaces of the gate electrodes 25, 29A and 29B.

[0200] As illustrated in FIG. 37, using a photoresist film (notillustrated) that has been patterned by photolithography as a mask, an ntype impurity (for example, P) is introduced into the p type well 4 onone side of the gate electrode 25 by ion implantation, followed by heattreatment.

[0201] After removal of the photoresist film, a new photoresist film(not illustrated) is formed over the regions 1A, 1C, 1E2 and 1D. Usingthis photoresist film as a mask, a p type impurity (for example, BF₂) isintroduced into the n type well 3 by ion implantation, whereby a p⁻ typesemiconductor region 31 is formed.

[0202] After removal of the photoresist film from the regions 1A, 1C,1E2 and 1D, another photoresist film (not illustrated) is formed overthe regions 1B and 1F. Using the photoresist film as a mask, an n typeimpurity (for example, P) is introduced into the p type well 4 by ionimplantation to form an n⁻ type semiconductor region 32. Then, thephotoresist film is removed from the regions 1B and 1F.

[0203] As illustrated in FIG. 38, a silicon oxide film is then depositedover the semiconductor substrate 1 by CVD. By anisotropic etching of thesilicon oxide film, side wall spacers 33 are formed by leaving thesilicon oxide film on the side walls of the gate electrodes 29A, 29B,25, 10E2, 10D and 10F.

[0204] A photoresist film (not illustrated) is then formed over theregions 1B and 1F and over the gate electrodes 29A, 25, 10E2 and 10D, soas to cover, with the photoresist film, a predetermined range of the n⁻type semiconductor region 32 on one side of the gate electrode 10D.Using the photoresist film as a mask, an n type impurity (for example,P) is then introduced into the p type well 4 by ion implantation.

[0205] After removal of the photoresist film, another photoresist film(not illustrated) is formed over the regions 1A, 1C, 1E2 and 1D and overthe gate electrodes 29B and 10F, so as to cover, with the photoresistfilm, a predetermined range of the p⁻ type semiconductor region 31 onone side of the gate electrode 10D. Using the photoresist film as amask, a p type impurity (for example, BF₂) is then introduced into the ntype well 3 by ion implantation. After removal of the photoresist film,the semiconductor substrate 1 is heat treated at about 900° C., wherebya p⁺ type semiconductor region 34 and n⁺ type semiconductor regions 35and 35A are formed. By these steps, a 5V type nMISQA, a 5V type pMISQB,a MISQC which will constitute a memory cell of a flash memory, ahigh-breakdown-voltage loading nMISQE2, a high-breakdown-voltageone-side offset nMISQD and a high-breakdown-voltage one-side offsetpMISQF can be formed in the regions 1A, 1B, 1C, 1E2, 1D and 1F,respectively.

[0206] As illustrated in FIG. 39, a silicon oxide film 36 of about 150nm thick is then deposited over the semiconductor substrate 1 by CVD.The silicon oxide film 36 is then dry etched using a photoresist film(not illustrated) that has been patterned by photolithography as a mask,whereby a contact hole 38A reaching the n⁺ type semiconductor region 35Ais formed in the silicon oxide film 36.

[0207] After removal of the photoresist film, an amorphous Si film isdeposited over the semiconductor substrate 1 by CVD, thereby embeddingthe contact hole 38A with the amorphous Si film. A polycrystalline Sifilm is then formed by heat treatment of this amorphous Si film. By dryetching using a photoresist film (not illustrated) that has beenpatterned by photolithography as a mask, the polycrystalline Si film ispatterned to form an interconnect TG. The semiconductor substrate 1 isthen heat treated, whereby a silicon oxide film 36A is formed over thesurface of the interconnect TG.

[0208] As illustrated in FIG. 40, a BPSG film 37 is deposited over thesemiconductor substrate 1 by CVD, followed by heat treatment of thesemiconductor substrate at about 900° C. in an N₂ atmosphere toplanarize the surface of the BPSG film 37.

[0209] Through a photoresist film (not illustrated) that has beenpatterned by photolithography, the BPSG film 37, silicon oxide film 36and gate insulating films 8, 17 are dry etched, whereby a contact hole38 is formed.

[0210] After removal of the photoresist film used for perforation of thecontact hole 38, an MoSi (molybdenum silicide) film of about 30 nm thickis deposited in the contact hole 38 and over the BPSG film by sputteringto form a barrier conductor film. Over the barrier conductor film, ametal film to embed therewith the contact hole 38 is deposited bysputtering. This metal film is composed mainly of Al (aluminum) andcontains Cu (copper). An antireflective film is then formed bydepositing an MoSi film over the metal film. The barrier conductor filmhas a function of preventing diffusion of the Al in the metal film intothe BPSG film 37 and silicon oxide film 36, while the antireflectivefilm serves to prevent irregular reflection upon formation of aphotoresist film over the antireflective film in the subsequent step.

[0211] By dry etching through a photoresist film (not illustrated) thathas been patterned by photolithography, the antireflective film, metalfilm and barrier conductor film are patterned to form an interconnect39, whereby the flash memory of this Embodiment is fabricated.

[0212] The present invention so far has been described specificallybased on embodiments of the invention. It is needless to say that thepresent invention is not limited to the embodiments, but can be modifiedto an extent not departing from the gist of the invention.

[0213] For example, use of ultrapure water prepared in theabove-described embodiment for a cleaning step of a semiconductorsubstrate during fabrication of a flash memory was described, but it canbe applied to a cleaning step employed during the fabrication of asemiconductor integrated circuit device (for example, logic circuit),other than a flash memory.

[0214] Of the features of the inventions disclosed by the presentapplication, effects available by representative ones will be describedsimply below.

[0215] It is possible to prevent run-off of ionized amine into theultrapure water in the step of preparing ultra pure water to be used forthe fabrication of a semiconductor integrated circuit device, making itpossible to prevent a lowering of the breakdown voltage of a gateinsulating film, which will otherwise occur due to the formation ofunevenness at the interface between the gate insulating film and thesemiconductor substrate.

What is claimed is:
 1. A method of fabrication of a semiconductorintegrated circuit device, comprising the steps of: (a) feeding acleaning apparatus with ultrapure water through a filter having a cationremoving property; and (b) cleaning, with the ultrapure water fedthrough said filter, a main surface of a wafer on which a device is tobe formed and which includes a portion from which a single crystalregion having silicon as a principal component is exposed.
 2. Afabrication method according to claim 1, wherein said filter is a cationremoving filter.